17-GHZ DIRECTIONAL COUPLER OPTICAL MODULATOR

The design of our high-speed directional coupler modulators at 0.83 mu m used a semi-vectorial finite difference solver to obtain the odd an d even mode optical propagation constants in the AlGaAs waveguide stru cture and a quasistatic finite difference code to obtain the RF charac teristics of the electrode structure, which was an asymmetric coplanar waveguide modified capacitance loading. The measured drive voltage of the modulators, for 10-90% response, varied between 22 and 27 V, comp ared with the theoretical value of 25 V. The 3 dB bandwidth of 17 GHz was obtained for this capacitive-loaded design, with 2500 mm interacti on length, and is in good agreement with the predicted result.